From the collection of Maureen Spaulding "Preserving Historic Bridges"  by John W. Snyder   Congress hereby finds and declares it to be in the national interest to encourage the rehabilitation, reuse and preservation of bridges significant in American history, architecture, engineering, and culture.  Historic bridges are important links to our past, serve as safe and vital transportation routes to the present, and can represent significant resources for the future.  Federal Surface Transportation Act of 1987   As part of the larger historic preservation movement, public interest in the significance of America's historic bridges began to grow in the early 1970s, beginning with interest in wooden covered bridges and their evocation of Americana and expanding into a larger concern for historic bridges of all types.  The public came to see historic bridges as representations of important developments in engineering technology and as essential components of larger historic districts and regions.   At the same time, the federal government expanded transportation programs to upgrade the infrastructure of American's highway system.  As a result, preservationists became aware of the enormous number of historic bridges scheduled for demolition using these-and other-funding sources.   The operation of a safe and comprehensive national highway system has long had broad political support, resulting in such initiatives as the Federal Highway Administration's (FHWA) Special Bridge Replacement Program and its successor, the Highway Bridge Replacement and Rehabilitation Program (HBRRP). Most transportation agencies hold that bridges have a life span of 50 years and, based on recent estimates by FHWA, officials consider nearly 225,000 of America's 576,000 highway bridges to be structurally deficient or functionally obsolescent and therefore eligible for replacement or upgrading through rehabilitation.   The threats to America's historic bridges are many.  Deferred maintenance leads to physical deterioration, as does increased traffic volume or weight for which the designers never calculated.  De-icing salts and chemicals can attack metal elements. Natural disasters such as floods may sweep bridges away, or so undermine their foundations as to lead to their collapse.  Earthquakes can bring sudden, severe damage or catastrophic collapse.  Seemingly unrelated actions such as local zoning changes can alter traffic patterns, either overburdening existing bridges and subsequently leading to proposals for new bridges, or leaving them carrying so little traffic that officials may view them as redundant and unnecessary.   The most important element in the successful, long-term preservation of historic bridges is strong local support.  Because most laws and regulations relating to bridge preservation issues concern federally-funded or authorized activities, local support should be sufficiently visible to impress local, state, and federal officials.  Public understanding of the importance of historic bridges, as well as familiarity with federal programs to encourage preservation, is key to the successful rehabilitation and reuse of historic bridges. Click here to go to the HAER site The Historic American Buildings Survey (HABS) and the Historic American Engineering Record (HAER) collections are among the largest and most heavily used in the Prints and Photographs Division of the Library of Congress. The collections document achievements in architecture, engineering, and design in the United States and its territories through a comprehensive range of building types and engineering technologies. Administered since 1933 through cooperative agreements with the National Park Service, the Library of Congress, and the private sector, ongoing programs of the National Park Service have recorded America's built environment in multiformat surveys comprising more than 350,000 measured drawings, large-format photographs, and written histories for more than 35,000 historic structures and sites dating from Pre-Columbian times to the twentieth century. This online presentation of the HABS/HAER collections includes digitized images of measured drawings, black-and-white photographs, color transparencies, photo captions, data pages including written histories, and supplemental materials.  To go the Schell Bridge's documentation, click on this web site, http://lcweb2.loc.gov/ammem/hhquery.html . Type in "Schell Bridge" and up will pop an analysis of the bridge AND hi-res tiff files from numerous angles.  Low-res, thumb-nailed versions of those pictures are seen below. Detail of lower chord connection to endpost at southeast corner Detail of Bearing shoe connection at southeast corner Detail of east portal, showing Gothic detailing Long oblique view from northeast abutment, looking west detail of lower chord and piers, looking southwest detail of floor system from river bank, looking northwest A Glossary of Bridge Terms Abutment:  The part of the substructure of a bridge that supports the ends of a single span, or the extreme ends of a multi-outer structure.   Chord:  The main outer structural member of a truss.   Compression members:  Generally still, heavy members that withstand pressures that tend to push them together; may be made of timber, or iron or steel, or concrete.   Covered bridge:  A bridge, usually timber, with a roof and sides providing weather protection for the truss and other parts.   Deck:  The roadway surface of a bridge.  Also, a type of bridge where the roadway rests atop the bridge framework or superstructure.   Girder:  A large beam that acts as a primary support, receiving loads from floor beams and stringers.  Also, a bridge type where the deck is supported by longitudinal structural members (girders).   Lattice truss:  A truss made up of a system of relatively light, crosshatched diagonal members.   Pier:  The part of a bridge substructure that supports the ends of the spans of a multi-span superstructure at intermediate locations between the abutments.   Pin-connected:  A type of early truss construction in which the truss members were connected by iron or steel pins, or bolts.   Portal:  The entrance to a bridge, especially a through truss or through arch.   Reinforced concrete:  Concrete with embedded steel reinforcing bars that bond to the concrete and add tensile strength to its inherent compressive strength.   Slab:  A type of bridge, usually short, in which the deck and its support are integral.   Substructure:  The abutments, piers, bents and footings that alone or in combination support the superstructure of the bridge.   Superstructure:  The portion of a bridge that receives traffic loads, in turn transferring those loads and it own and its own load to the substructure. The superstructure may consist of girders, trusses, slabs, or other types of construction.   Suspension:  A bridge type with the roadway suspended from high towers, using a combination of cables, chains, or eyebars.   Tension members: Members of a bridge that resist forces tending to pull them apart; usually made of iron or steel due to superior tensile strength.   Through truss:  A truss in which the deck is  nearly at the bottom of the superstructure, with traffic passing between the trusses.   Truss:  A bridge type whose framework is composed of members forming a triangle or system of triangles that support both the weight of the bridge (dead load) and the traffic (live) loads.